New kernel branch for XO-1 and XO-1.5 development

[Deepak Saxena]

I've spent some time merging the XO-1 and XO-1.5 kernels into a new
branch and made some tweaks to the in-kernel RPM build scripts. From 
now on, all development for both XO-1 and XO-1.5 will be done on the 
olpc-2.6.30 branch of the olpc-2.6 repository [1]. As Linus releases
new kernels, I will be rebasing [2] the OLPC changes on top of Linus'
releases and creating new olpc-${kernelversion} branches to make it
easier to move our code forward and upstream.

Since the kernels for the two generations of XO boards have been
merged, I've had to change the commands for building RPMs and
kernels. These are:

make xo_1_defconfig    : configure kernel for OLPC XO-1
make xo_1.5_defconfig  : configure kernel for OLPC XO-1.5
make xo_1-kernel-rpm   : build XO-1 kernel RPM
make xo_1_5-kernel-rpm : build XO-1.5 kernel RPM
make olpc-kernel-rpm   : build both XO-1 and XO-1.5 kernel RPMs

To differentiate between an XO-1 and XO-1.5 RPM, the generation
name is now inserted into the RPM name. For example:

kernel-2.6.30_xo1-20090708.1.olpc.1fd3a66.i586.rpm   <- XO-1 RPM
kernel-2.6.30_xo1.5-20090708.1.olpc.1fd3a66.i586.rpm <- XO-1.5 RPM

Note that currently there is nothing keeping anyone from installing a
kernel meant for one gen machine on a different gen machine. Just 
don't do that. :)

I've also added the ability to build RPMs from trees that have
non-commited changes. If this is done, the RPM will be tagged
as dirty:

kernel-2.6.30_xo1-20090708.1.olpc.1fd3a66_DIRTY.i586.rpm

I will update wiki with this information.

Enjoy,
~Deepak

[1] dev.laptop.org:/git/olpc-2.6

[2] http://www.kernel.org/pub/software/scm/git/docs/git-rebase.html
    for manpage, http://www.eecs.harvard.edu/~cduan/technical/git/git-5.shtml
    for a quick summary.